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Supernova

One of the most energetic explosive events known is a supernova. These occur
at the end of a star's lifetime, when its nuclear fuel is exhausted and it is
no longer supported by the release of nuclear energy. If the star is
particularly massive, then its core will collapse and in so doing will
release a huge amount of energy. This will cause a blast wave that ejects the
star's envelope into interstellar space. The result of the collapse may be,
in some cases, a rapidly rotating neutron star that can be observed many
years later as a radio pulsar.

While many supernovae have been seen in nearby galaxies, they are
relatively rare events in our own galaxy. The last to be seen was Kepler's
star in 1604.
This remnant has been studied by many X-ray astronomy satellites,
including ROSAT. There are,
however, many remnants of Supernovae explosions in our galaxy, that are
seen as X-ray shell like
structures caused by the shock wave propagating out into the
interstellar medium. Another famous remnant is the Crab Nebula which exploded
in 1054. In this case a pulsar is seen which rotates 30 times a second and
emits a rotating beam of X-rays (like a lighthouse). Another dramatic
supernova remnant is the
Cygnus Loop.